1. Field of the Invention
This invention relates to a method of exposing and an apparatus therefor. More particularly, the present invention relates to an exposure apparatus of, for example, a slit scanning exposure type and an exposure method advantageously applicable to such apparatus.
2. Related Background Art
Projection type exposure apparatus has been used in manufacturing semiconductor devices, liquid crystal displays and thin-film magnetic heads through a photolithography process, in which patterns of a photomask or a reticle (hereinafter, referred generally to as xe2x80x9creticlexe2x80x9d) are transferred to the surface of a substrate (wafer, glass plate, etc.) coated with a photosensitive coating.
The conventional projection type exposure apparatus commonly used is a reduction projection type exposure apparatus (stepper) that moves individual shots on the wafer successively to an exposing field of a projection optical system to reproduce pattern images of the reticle on the shots using a photographic step-and-repeat process.
In the typical steppers, a wafer coordinate system is corresponded to a reticle coordinate system (reticle alignment).
Some steppers comprise an alignment microscope of an off-axis type provided at one side surface of the projection optical system to detect a position of the alignment mark (wafer mark) formed as a correspondence to each shot on the wafer. In such a case, the shot on the wafer is determined within the exposing field of the projection optical system according to the position of the associated wafer mark detected on the alignment microscope. Accordingly, so-called base line amount should be obtained previously that represents a distance between a reference point (such as an exposure center) within the exposing field of the projection optical system and a reference point in an observing field of the alignment microscope of the off-axis type.
The reticle alignment and the base line measurement are disclosed in detail in, for example, Japanese Patent Application Laid-Open No. 4-324923 (corresponding to U.S. patent application Ser. No. 872,750 (filed on Apr. 21, 1992)).
In recent years, fine patterns for the semiconductor devices require resolution of the projection optical system to be improved. To improve the resolution, exposing light may be shifted to a shorter wavelength or alternatively, the number of openings of the projection optical system may be increased. In any event, it has been difficult to maintain an image quality (such as distortion and image plate deformation) on the entire exposing field with a predetermined accuracy when it is intended to ensure as same exposing field as conventional arts. With this respect, the projection type exposure apparatuses based on so-called slit scanning exposure type have taken a favorable turn.
In the projection type exposure apparatus of the slit scanning exposure type, the reticle and the wafer are scanned relative to and synchronous with a rectangular or arc-shaped illumination field (hereinafter, referred to as a xe2x80x9cslit-shaped illumination fieldxe2x80x9d) to transfer the patterns of the reticle on the wafer. The slit scanning exposure type thus makes it possible to reduce the exposing field of the projection optical system as compared with the stepper type, provided that the reproduced patterns are equal in area to those reproduced using the stepper type. This may improve the accuracy of the image quality within the exposing field. A six-inch size is dominant for the conventional reticles while a one-fifth factor is dominant as the projection magnification of the projection optical system. At the magnification of one-fifth factor, the six-inch reticle may sometimes be insufficient for recent circuit patterns of the semiconductor device having the increased area. As a result, the projection optical systems should so designed that the projection magnification of the projection optical system is changed to, for example, quarter factors. To comply with requirements for such reproduced patterns having the increased areas the slit scanning exposure type can advantageously be applied.
In this event, the alignment method based on the reticle and wafer coordinate systems used in the conventional steppers may be unfavorable when being applied to the projection type exposure apparatus of the slit scanning type. The projection magnification of quarter factors adversely affects the accuracy of the alignment because the alignment becomes more sensitive to writing errors of the circuit patterns on the reticle.
A technique has been suggested in the above mentioned U.S. patent application Ser. No. 872,750 (filed on Apr. 21, 1992) to measure a rotation angle of the reticle by means of measuring simultaneously the amount of displacement of two or more measuring marks rather than moving the wafer stages in the wafer. However, the idea of measuring the rotation angle using the simultaneous measuring of the measuring marks cannot be applied to scanning directions of the projection type exposure apparatus of the slit scanning exposure type. Thus, there is a disadvantage that it is impossible to measure the rotation angle of the reticle and wafer coordinate systems and orthogonal amount of the coordinates of these coordinate systems.
As for the method of measuring the base line amount between the reference position within the exposing field of the projection optical system and the reference position of the alignment system of the off-axis type, the conventional measuring method using a pair or marks on the reticle in the stepper is disadvantageous, when it is applied to the projection type exposure apparatus of the slit scanning exposure type with no modification, in that the writing error of the reticle significantly affects the measurements.
With respect to these problems, the present invention is directed to provide an exposure method and an exposure apparatus capable of reducing affect of the writing error between the patterns on the reticle (mask), allowing positive alignment of the reticle coordinate system (mask coordinate system) and the wafer coordinate system (substrate coordinate system) in the exposure apparatus of the slit scanning exposure type.
In light of this, speed of operation may sometimes be considered to be more important than the accuracy of alignment depending on the process. With this respect, another object of the present invention is to provide an exposure method and an exposure apparatus capable of aligning the reticle coordinate system (mask coordinate system) with the wafer coordinate system (substrate coordinate system) at a higher throughput.
Yet another object of the present invention is to provide an exposure method and an exposure apparatus capable of reducing affect of the writing error between the patterns on the reticle (mask), allowing positive measurement of the base line amount between the reference point in the exposing field of the projection optical system and the reference point of the alignment system in the exposure apparatus of the slit scanning exposure type.
Still another object of the present invention is to provide an exposure method and an exposure apparatus in which the alignment between the reticle coordinate system (mask coordinate system) and the wafer coordinate system (substrate coordinate system) as well as the base line amount are obtained for exposure.
In a case where the base line measurement is performed for every predetermined number of wafer replacements, speed of operation may be considered to be more important than the accuracy of alignment. At the same time, the reticle coordinate system (mask coordinate system) is preferably aligned to the wafer coordinate system (substrate coordinate system). With this respect, another object of the present invention is to provide an exposure method and an exposure apparatus capable of aligning the reticle coordinate system (mask coordinate system) to the wafer coordinate system (substrate coordinate system) and of measuring the base line therefor at a higher throughput for every predetermined number of wafer replacements.
It is yet another object of the present invention to provide an exposure method and an exposure apparatus using a plurality of measuring reticle marks to reduce affect of, for example, the writing errors between patterns on the reticle (mask).
It is still another object of the present invention to provide an exposure method and an exposure apparatus capable of aligning the reticle coordinate system (mask coordinate system) to the wafer coordinate system (substrate coordinate system) and of measuring the base line therefor with a high accuracy in consideration of an error component to a relative scanning direction of the mask to the wafer.
In an exposure method according to a first aspect of the present invention, it is provided with an exposure method of transferring, using an optical system for illuminating a mask having patterns to be transferred to a substrate and a projection optical system for projecting images of the patterns to the substrate, the patterns on the mask to the substrate on a stage through the projection optical system by means of scanning the mask and the substrate synchronously relative to the projection optical system, wherein the method comprises the steps of: providing a plurality of measuring marks on the mask formed along a relative scanning direction, and providing a plurality of reference marks formed on the stage corresponding to the measuring marks, respectively; moving the mask and the substrate synchronously in the relative scanning direction to measure successively a displacement amount between the measuring marks on the mask and the reference marks; and obtaining a correspondence relation between a coordinate system on the mask and a coordinate system on the stage according to the displacement amount.
In an exposure method according to a second aspect of the present invention, it is provided with an exposure method of transferring, using an exposure apparatus having an optical system for illuminating a mask having patterns to be transferred to a substrate, a mask stage for holding the mask, a substrate stage for holding the substrate, a projection optical system for projecting images of the patterns to the substrate, and an alignment system having its detection center at a position away from the optical axis of the projection optical system at a predetermined distance, the patterns to the substrate through the projection optical system by means of scanning the mask and the substrate synchronously relative to the projection optical system, wherein the method comprises the steps of providing a plurality of measuring marks formed on the mask along a relative scanning direction;. providing first reference marks corresponding to a part of the measuring marks and second reference marks corresponding to the first reference marks, respectively, the first and the second reference marks being formed on the stage, the second reference marks being away from the first reference marks at a given distance that is recognized previously; moving the mask to the relative scanning direction with the second reference marks observed through the alignment system to measure successively a displacement amount between the measuring marks on the mask and the first reference marks; and obtaining a distance between a reference point within an exposing field of the projection optical system and the detection center according to the displacement amount between the measuring marks and the first reference marks, to a displacement amount of the second reference marks observed through the alignment system, and to the given distance previously recognized.
In an exposure method according to a third aspect of the present invention, it is provided with an exposure method of transferring, using an exposure apparatus having an optical system for illuminating a mask having patterns to be transferred to a substrate, a mask stage for holding the mask, a substrate stage for holding the substrate, a projection optical system for projecting images of the patterns to the substrate, and an alignment system having its detection center at a position away from the optical axis of the projection optical system at a predetermined distance, the patterns to the substrate through the projection optical system by means of scanning the mask and the substrate synchronously relative to the projection optical system, wherein the method comprises the steps of providing a plurality of measuring marks formed on he mask along a relative scanning direction; providing first reference marks corresponding to each of the measuring marks and second reference marks corresponding to the first reference marks, respectively, the first and the second reference marks being formed on the stage, the second reference marks being away from the first reference marks at a given distance that is recognized previously; moving the mask and the substrate to a scanning direction to measure successively a displacement amount between the measuring marks on the mask and the first reference marks; moving the mask and the substrate relatively to the scanning direction to measure successively a displacement amount of the second reference marks; and obtaining, a distance between a reference point within an exposing field of the projection, optical system and the detection center according to the displacement amount between the measuring marks and the first reference marks, to a displacement amount of the second reference marks observed through the alignment system, and to the given distance previously recognized.
In an exposure method according to a fourth aspect of the present invention, it is provided with an exposure method of transferring, by means of illuminating an illumination area of a predetermined shape using an illumination light to scan a mask and a substrate synchronously relative to the illumination area of a predetermined shape, patterns on the mask within the illumination area of the predetermined shape through a projection optical system to the substrate on a stage, wherein the method comprises, with a plurality of measuring marks formed on the mask along a relative scanning direction and reference marks formed on the stage corresponding to the measuring marks, a first step for measuring a displacement amount between a part of the measuring marks and the reference marks corresponding to the part of the measuring marks, respectively; a second step for moving the mask and the substrate synchronously to the relative scanning direction to measure successively a displacement amount between the measuring marks on the mask and the reference marks corresponding to the measuring marks; and a third step for selecting one of the first and the second steps to obtain a corresponding relation between a coordinate system on the mask and a coordinate system on the stage according to the displacement amount between the measuring marks and the reference marks, respectively, obtained at the selected step.
In an exposure method according to a fifth aspect of the present invention, it is provided with an exposure method of transferring, using an exposure apparatus having an optical system for illuminating an illumination area of a predetermined shape using an illumination light, a mask stage for holding a mask provided with patterns to be exposed, a substrate stage for holding a substrate, a projection optical system for projecting the patterns on the mask to the substrate, an alignment system having its detection center at a position away from the optical axis of the projection optical system at a predetermined position, the patterns on the mask in the illumination area of the predetermined shape through the projection optical system to the substrate by means of scanning the mask and the substrate synchronously relative to the illumination area of the predetermined shape, wherein the method comprises, with a plurality of measuring marks formed on the mask along a relative scanning direction and a plurality of first reference marks corresponding to the measuring marks and second reference marks corresponding to the first reference marks, the first and the second reference marks being formed on the stage, the second reference marks being away from the first reference mark at a given distance that is recognized previously, a first step for measuring a displacement amount between a part of the measuring marks on the mask and the first reference marks corresponding to the part of the measuring marks, respectively, and measuring a displacement amount between the second reference marks corresponding to the part of the first reference mark; a second step for moving the mask and the substrate in synchronism with the scanning direction to measure successively a displacement amount between the measuring marks and the first reference marks corresponding to the measuring marks, respectively, and a displacement amount of the second reference marks; a third step for selecting one of the first and the second step; and a fourth step for obtaining a corresponding relation between a coordinate system on the mask stage and a coordinate system on the substrate stage and a distance between a reference point within an exposing field of the projection optical system and the detection center according to information obtained during the step selected at the third step and a given distance previously recognized.
In an exposure method according to a sixth aspect of the present invention, it is provided with an exposure method of transferring, using an exposure apparatus having an optical system for illuminating an illumination area of a predetermined shape using an illumination light, a mask stage for holding a mask provided with patterns to be exposed, a substrate stage for holding a substrate, a projection optical system for projecting the patterns on the mask to the substrate, an alignment system having its detection center at a position away from the optical axis of the projection optical system at a predetermined position, the patterns on the mask in the illumination area of the predetermined shape through the projection optical system to the substrate by means of scanning the mask and the substrate synchronously relative to the illumination area of the predetermined shape, wherein the method comprises, with a plurality of measuring marks formed on the mask along a relative scanning direction and a plurality of first reference marks corresponding to the measuring marks and second reference marks corresponding to the first reference marks, the first and the second reference marks being formed on the stage, the second reference marks being away from the first reference mark at a given distance that is recognized previously, for every replacement of predetermined number of substrates, a step for measuring a displacement amount between a part of the measuring marks on the mask and the first reference marks corresponding to the part of the measuring marks, respectively, and measuring a displacement amount between the second reference marks corresponding to the part of the first reference mark; and a step for obtaining a corresponding relation between a coordinate system on the mask and a coordinate system on the stage and a distance between a reference point within an exposing field of the projection optical system and the detection center according to a displacement amount between one measuring mark and one first reference mark, to a displacement amount of the second reference marks, and to the given distance recognized previously.
According to the first exposure method of this invention, it is possible to reduce affect of the writing error of the measuring marks on the mask by means of obtaining a parameter (such as the magnification, a scaling in the scanning direction, rotation, degree of parallelism in the scanning direction, and offsets in an X direction and a Y direction) for use in aligning the mask coordinate system with the substrate coordinate system by using the least square approximation by means of, finally, matching the displacement obtained, for example, at each position of the measuring mark on the mark.
According to the second exposure method, it is possible to measure positively the base line amount or the distance between the reference point of the projection optical system and the reference point of the alignment system by means of reducing the writing error of the measuring marks on the mask through measurement regarding to the measuring marks on the mask side.
According to the third exposure method, a plurality of first reference marks are formed on a reference mark member with being correspondent with the measuring marks, respectively, on the mask. In addition, a plurality of second reference marks are formed at such a distance that corresponds to the distance between the reference point within the exposing field of the projection optical system and the reference point of the alignment system from the first reference marks. Accordingly, the base line amount can be measured more positively because the balancing is made across the reference marks.
According to the fourth exposure method, a simple measuring steps based on a quick mode are selected, which allows calculation of the corresponding relation between the coordinate system on the mask and the coordinate system on the stage at a higher throughput depending on the necessities.
According to the fifth exposure method, a simple measuring steps based on a quick mode are selected, which allows calculation of the corresponding relation between the coordinate system on the mask and the coordinate system on the stage as well as the base line amount at a higher throughput depending on the necessities.
According to the sixth exposure method, a simple measuring steps based on a quick mode are performed for every exposure of a predetermined number of substrates, which allows calculation of the corresponding relation between the coordinate system on the mask and the coordinate system on the stage as well as the base line amount at a higher throughput when many substrates are subjected to exposure continuously through the scanning method.
In an exposure method according to a seventh aspect of the present invention, it is provided with an exposure method for transferring, by means-of illuminating an illumination area of a predetermined shape using an illumination light and scanning a mask and a substrate synchronously relative to the illumination area of the predetermined shape, patterns on the mask in the illumination area of the predetermined shape to the substrate on a stage through a projection optical system, wherein the method comprises, with a plurality of measuring marks formed on the mask along a relative scanning direction and a plurality of reference marks formed on the stage corresponding to a part of the measuring marks, the steps of moving the mask to the relative scanning direction to measure successively a displacement amount between the measuring marks on the mask and the reference marks; and obtaining a corresponding relation between a coordinate system on the mask and a coordinate system on the stage.
In an exposure method according to an eighth aspect of the present invention, it is provided with an exposure method for transferring, using an exposure apparatus having an optical system for illuminating an illumination area of a predetermined shape using an illumination light, a mask stage for holding a mask provided with patterns to be exposed, a substrate stage for holding a substrate, a projection optical system for projecting the patterns on the mask to the substrate, an alignment system having its detection center at a position away from the optical axis of the projection optical system at a predetermined position, the patterns on the mask in the illumination area of the predetermined shape through the projection optical system to the substrate by means of scanning the mask and the substrate synchronously relative to the illumination area of the predetermined shape, wherein the method comprises the steps of forming on the substrate stage a reference mark detectable by the alignment system to measure a displacement amount of the reference marks by the alignment system; entering a mark error of the mask; and obtaining a corresponding relation between a coordinate system on the mask stage and a coordinate system on the substrate stage, and a distance between a reference pint within an exposing field of the projection optical system and the detection center.
In an exposure apparatus according to a first aspect of the present invention, it is provided with an exposure apparatus comprising a mask stage for holding a mask provided with patterns to be transferred; a substrate stage for holding a substrate; an optical system for illuminating the mask using an illumination light; a projection optical system for projecting images of the patterns on the mask to the substrate; and a first mark detecting system for detecting a mask mark formed at a predetermined position on the mask within an exposing field of the projection optical system, the exposure apparatus being for use in scanning the mask and the substrate synchronously relative to the projection optical system to transfer the patterns on the mask to the substrate through the projection optical system, wherein the apparatus further comprises a reference plate provided on the substrate stage, the reference plate comprising a plurality of first reference marks detectable by the first mark detecting system through the projection optical system; a plurality of measuring marks provided on the mask, each of the measuring marks being provided along a relative scanning direction with being correspondent with the reference mark; a driving control system for use in observing a part of the first reference marks and a part of the measuring marks through the first mark detecting system to move the mask stage and the substrate stage to the relative scanning direction such that a displacement amount between the measuring marks on the mask and the reference marks is measured successively; and calculating means for calculating a corresponding relation between a coordinate system on the mask stage and a coordinate system on the substrate stage.
In an exposure apparatus according to a second aspect of the present invention, it is provided with an exposure apparatus comprising a mask stage for holding a mask provided with patterns to be transferred; a substrate stage for holding a substrate; an optical system for illuminating the mask using an illumination light; a projection optical system for projecting images of the patterns on the mask to the substrate; and a first mark detecting system for detecting a mask mark formed at a predetermined position on the mask within an exposing field of the projection optical system, the apparatus being for use in scanning the mask and the substrate synchronously relative to the projection optical system to transfer the patterns on the mask to the substrate through the projection optical system, wherein the apparatus further comprises a reference plate provided on the substrate stage, the reference plate comprising a plurality of first reference marks detectable by the first mark detecting system through the projection system and second reference marks provided with being away from the first reference marks at a given distance that is recognized previously; a plurality of measuring marks provided on the mask, each of the measuring mask being provided along the relative scanning direction with being correspondent with the first reference mark; a driving control system for use in moving the mask stage and the substrate stage to the relative scanning direction such that the part of the measuring marks and the part of the reference marks are observed through the first mark detecting system and a displace amounts are measured successively between the measuring marks on the mask and the reference marks as well as between the second reference marks with one of a plurality of second reference marks being observed through a second mark detecting system; and calculating means for calculating a corresponding relation between a coordinate system on the mask stage and a coordinate system on the substrate stage and a distance between a reference point within an exposing field of the projection optical system and the detection center according to the displacement amounts measured.